The parking and entry/exit are better this year than ever before. With that being said, we went to Carowinds in the early 2000s for a 4th of July Fireworks show and have never been there since on the 4th. Back then it took us 3 hours to get out of the parking lot so I don't expect anything much different this year regardless of what they do. As others have said, there is no practical solution to so many people leaving at the exact same time.
On the topic of customer service, that is an area that I know a lot about. Some say it is all about the base (pay - pun intended), I disagree. While I agree that a company achieving over $1 billion in net revenue should be paying seasonal employees better, that is not what makes for good customer service. There are too many factors to list, so many that I could write a book (hey, wait....

) but it kind of boils down to training, treating the employees as family, boosting morale, coaching, having quality supervisors, etc.
I agree that McDonalds and Chick-fil-a are essentially the same. They pay about the same and draw from the same pool of applicants. However, one penny pinches and focuses solely on the bottom line where the other one focuses on customer service, leading to what usually is two completely different dining experiences (while both serve equally unhealthy meals loaded with fat, saturated fat, and sodium)
Many moons ago I ran a Subway restaurant and took a restaurant that for five years had hardly ever made a profit into one that broke the all-time sales record by over 25% and then maintained the previous sales record and made a profit every single week until I left. It took less than 2 months to turn the restaurant around, and all of my employees were paid minimum wage. The secret? I kept a super clean store, trained and rewarded my employees for great customer service, always kept the food fresh, and treated both the employees and customers like family.
I'm not saying that Carowinds does or doesn't have any of the above, just speaking from my personal experience of 20+ years in customer service. I have absolutely no insight into how they run their crews. My opinion is that most companies are (or should see themselves) as a customer service company regardless of what good or service they provide and I carry that with me no matter where I work. It has served me well over the years.